Power supply apparatuses for arc-utilizing apparatuses may be used with one of higher-voltage providing commercial AC power supplies providing voltages having effective values of the order of, for example, 400 V, e.g. 380 V, 415 V, 440 V and 460 V, or with one of lower-voltage providing commercial AC powers supplies providing voltages having effective values of the order of, for example, 200 V, e.g. 200 V, 208 V and 230 V. In some areas, both higher,. voltage and lower-voltage providing commercial AC power supplies are used. In such areas, it is difficult for a person to determine which power supply apparatus should be brought with him, one operable from a higher commercial AC voltage or one operable from a lower commercial AC voltage. Also, manufacturers have to provide two types of power supply apparatuses, one for a lower AC voltage, one for a higher AC voltage. In addition, sale agents must have both types of power supply apparatuses in stock.
Therefore, a power supply apparatus which can operate from either higher or lower commercial AC voltage has been desired.
An example of such power supply apparatuses is disclosed in U.S. Pat. No. 5,272,313 (Karino et al.) issued on Dec. 21, 1993 and assigned to the assignee of the present application. The apparatus shown in this U.S. patent includes an input-side rectifier which rectifies a voltage from a commercial AC power supply. When the commercial AC power supply coupled to the input-side rectifier is one which supplies one of higher voltages, the output voltage of the rectifier ig smoothed by a series combination of first and second capacitors. If the commercial AC power supply supplies one of lower voltages, the first and second capacitors are connected in parallel with each other, and the output voltage of the rectifier is smoothed by this parallel combination. First and second inverters are connected in parallel with the first and second capacitors, respectively. Each of the first and second inverters converts a DC voltage developed across the associated capacitor into a high-frequency voltage. The high-frequency voltages from the first and second inverters are voltage-transformed by first and second transformers, respectively, and the output voltages of the transformers are combined and converted into a DC voltage by a high-frequency-to-DC converter.
The power supply apparatus of Karino et al. can be used with either higher-voltage providing commercial AC power supplies or lower-voltage providing commercial AC power supplies. The first and second inverters of Karino et al. use IGBTs, each of which has a collector-emitter voltage rating of 600 V. This voltage of 600 V is about two times the maximum value of the input voltage to the first and second inverters. However, some higher-voltage providing commercial AC power supplies may provide a voltage of 575 V, which is higher than 460 V, the highest one of the above-mentioned higher voltages. In this case, the input voltage to the first and second inverters is about 400 V, which means that a margin for increase of the collector-emitter voltage of the IGBTs of the first and second inverters is small, This would cause the power supply apparatus to be damaged when the input voltage undesirably increases. To avoid such damage, IGBTs having a collector-emitter voltage rating of 1200 V may be used, but such IGBTs have a poor switching characteristic and exhibits a large switching loss. Accordingly, a power supply apparatus using such high collector-emitter voltage rating IGBTs exhibits low efficiency.
U.S. Pat. No. 6,054,674 (Moriguchi et at) issued on Apr. 25, 2000 and assigned to the assignee of the present application discloses an improved power supply apparatus. The power supply apparatus of Moriguchi et al., too, employs an input-side rectifier, first and second capacitors and first and second inverters. The power supply apparatus includes also a voltage-lowering converter. When a commercial AC power supply providing a voltage of 575 V is connected to the input-side rectifier, the output voltage of the input-side rectifier is lowered by the voltage-lowering converter, and the lowered voltage is applied across the series combination of the first and second capacitors. When a commercial AC power supply providing a higher voltage other than 575 V is connected to the input-side rectifier, the input-side rectifier output voltage is applied as it is across the series combination of the first and second capacitors. When a lower-voltage providing commercial AC power supply is connected to the input-side rectifier, the first and second capacitors are connected in parallel, and the output voltage of the input-side rectifier is applied across the parallel combination of the first and second capacitors. Thus, a power supply apparatus operable with either higher-voltage providing commercial AC power supplies providing higher voltages including a voltage of 575 V or lower-voltage providing commercial AG power supplies is realized.
However, the power supply apparatus of Moriguchi et al. requires an additional voltage-lowering converter, which increases the cost. In addition, the voltage-lowering converter requires a large-capacitance semiconductor devices which can withstand a voltage of 575 V, which further increases the cost of the power supply apparatus.
An object of the present invention is to provide a power supply apparatus for arc-utilizing apparatuses which operates at a high efficiency and can be manufactured at a low cost.